In contrast to an on-cell touch technology, an in-cell touch technology refers to the technology of forming elements used for realizing touch-panel functions within liquid crystal pixels. The in-cell touch-screen, with advantages of high light-transmittance and high resistance to damages, becomes an important development direction for touch-screens in future. The existing in-cell touch technology has generally two types: capacitive type and photosensition type.
A common capacitive or photosensition touch-screen has disadvantages of reduced sensitivity and complexity in algorithms because its structure has requirements on touch pressure and light intensity. The operating principle of a capacitive touch-screen is that: because a finger press causes change in distance between the electrode plates of a capacitor and thus causes change in the capacitance value, and through detection on such change, the touch position is obtained. However, it is required a relatively large touch-pressing force to change the thickness of the screen, thus the capacitive type does not have high sensitivity. The operating principle of a photosensitive touch-screen is that: because a finger touch blocks the intensity of the light irradiated from the external to the photosensitive thin film transistor (TFT) and thus causes change in the inductive current of the photosensitive TFT, and through detection on such change, the touch position is obtained. However, due to finger shadow, light intensity changes are also caused in non-touched regions, the photosensitive elements therefore may be subjected to erroneous detection phenomenon due to the finger shadows, and also the photosensition type does not have high accuracy.